Justin Timberlake, who starred in the 2006 film Alpha Dog with the late actor, took to Twitter, writing, "Anton Yelchin. Genius actor. Amazing human being. Gone WAY too soon. May he rest in peace."

Yelchin's Star Trek co-star, Zachary Quinto, wrote on Instagram, "Our dear friend. Our comrade. Our Anton. One of the most open and intellectually curious people I have ever had the pleasure to know. So enormously talented and generous of heart. Wise beyond his years and gone before his time. All love and strength to his family at this impossible time of grief."

"Devastated to hear about the brilliant Anton Yelchin," said Chris Evans, who co-starred with the actor in the drama Fierce People. "He was thoughtful, kind, and gifted. My thoughts and prayers are with his family."

Yelchin's Star Trek co-star, John Cho, wrote, "I loved Anton Yelchin so much. He was a true artist - curious, beautiful, courageous. He was a great pal and a great son. I'm in ruins."

"Please send your love to Anton's family right now," he added in a second tweet. "They need it."

Star Trek director J.J. Abrams penned a note to Anton, which he shared via Twitter. "Anton – you were brilliant. You were kind. You were funny as hell, and supremely talented," the letter, hand-written in all-caps, read. "And you weren't here nearly long enough. Missing you… JJ."

Yelchin's good friend Kat Dennings tweeted, "Anton Yelchin was one of my best friends. Can't say anything that conveys what this feels like."

Paramount, the studio behind Star Trek, released a statement on Yelchin, saying, "All of us at Paramount join the world in mourning the untimely passing of Antony Yelchin. As a member of the Star Trek family, he was beloved by so many and he will missed by all. We share our deepest condolences with his mother, father and family."

The LAPD's Valley Traffic Division confirmed TMZ's first report of the death to ET. According to the LAPD, Yelchin's friends grew suspicious when he didn't meet them for a rehearsal on Saturday. When they arrived at his house at 1 a.m. local time, they found him pinned between his car, a mailbox, and a security gate.

"The speculation is that he got out of the car and it was in neutral and rolled back on him," the LAPD tells ET.